Water pollution is mainly caused by humans.

Garbage and other household
wastes are thrown into esteros and canals. Some households along
riverbanks dump their waste in the rivers.
Factories and industrial plants release their waste into bodies of water.
Smoke from vehicles contains sulfur oxide and nitrogen oxide. These
pollutants combine with moisture in the atmosphere which are collected in a
cloud. Water collected in this clouds is released in the form of acid rain.
Excess fertilizers from agricultural lands eventually end up in nearby bodies
of water. This enriches the water and causes algal bloom. Algal bloom is the
excessive growth of algae in the bodies of water. The process that causes
algal bloom is called eutrophication.
Bacteria use the dissolved oxygen in the water in decomposing dead plants
and algae. These bacteria compete with the organisms living in the water for
oxygen. As a result, organisms originally living in the body of water die due
to lack of oxygen.
Radioactive substances are really merely a special sub-class of chemical
pollutants, and by mass represent the smallest of the contributors to water
pollution; however, their potential for harm allows recognition as a separate
class. In fact, most discharge of radioactivity is not from the negligible
escape from nuclear power plants, but rather arises from agricultural
practices such as tobacco farming, where radioactive contamination of
phosphate fertilizer is a common method of introduction of radioactive
materials into the environment.
Common pathogenic microbes introduced into natural water bodies are
pathogens from untreated sewage or surface runof from intensive livestock
grazing. One of the most common disease agents is Giardia
labia , a parasitic protozoan common in fecal material of many fauna
including humans; this microbe is particularly insidious, due to its resistance
to conventional sewage treatment. This and other protozoans and bacteria
are important causes of illness and mortality in developing countries where
population density, water scarcity and inadequate sewage treatment
combine to occasion widespread parasitic and bacterial disease.

Water pollution is the contamination of natural water bodies by chemical,
physical, radioactive or pathogenic microbial substances. Adverse alteration
of water quality presently produces large scale illness and deaths,
accounting for approximately 50 million deaths per year worldwide, most of
these deaths occurring in Africa and Asia. In China, for example, about 75
percent of the population (or 1.1 billion people) are without access to

since their
sources may be construed as natural. Some
consider that water pollution may occur from natural causes such as
sedimentation from severe rainfall events. these point source discharges
typically afect the metabolism of aquatic fauna in adverse ways. chlorinated organic molecules arising from sewage or water
treatment plants or various acids which are the externalities of various
manufacturing activities. mostly arising from over-intense land use practices
and rubbish discarded from human manufacturing activity (e. The most obvious of physical pollutants are
excessive sediment load. biodiversity reduction and loss of ecosystem services. While these materials are not so harmful to human health as
chemicals or pathogens.
Common examples of such chemical water pollutants are mercury emanating
from mining activity. The most
problematic of water pollutants are microbes that induce disease. Widespread
consequences of water pollution upon ecosystems include species
mortality. which have
been discharged into natural water bodies.
including volcanic eruptions and algae blooms from natural causes constitute
a minute amount of the instances of world water pollution.g. natural causes.unpolluted drinking water.
. certain nitrogen compounds used
in agriculture. cause a
variety of harmful efects. however.
Physical water pollutants are either much larger particles or physical factors
such as temperature change.
bottles). they comprise the majority of visual impact of water
pollution. In the case of thermal pollution. both of which while not typically toxic. according to China's own standards.
Classes of water pollutants
Chemical water pollutants are generally atoms or molecules. plastic bags. but a preponderance of these
instances result from human intervention in the environment or human
overpopulation phenomena. usually by activities of humans.